Pakistan has detained dozens of suspected militants following the attack in Indian-administered Kashmir which sparked a crisis with India.
They include the son and brother of Masood Azhar, founder of militant group Jaish-e-Mohammad (JeM), which claimed responsibility for the suicide bombing.
Officials said 44 suspected militants are in "preventative detention".
Pakistan has been under international pressure to crack down on militant networks since the 14 February attack.
It triggered a crisis with India that threatened to escalate into military conflict, and Delhi said it had carried out air strikes on a JeM training camp in response.
Addressing the militant detentions, Pakistan's Interior Secretary Azam Suleman Khan told the BBC that if investigators find "evidence against them, they will be proceeded against," and if not they will be set free.
JeM is designated a terror organisation by India and the UN, as well as the UK and the US.
Pakistan said the arrests were not a result of any external pressure, though Indian officials have reacted with scepticism.
At least some of those held are thought to be named in an Indian dossier handed to the Pakistani authorities investigating last month's Pulwama suicide attack.
In the past, some militants have faced legal action in Pakistan, before later being released.
India accuses Pakistan of allowing militant groups to operate on its territory and says Pakistani security agencies played a role in the attack, which was claimed by JeM and killed 40 Indian troops.
Pakistan denies any role and has said it does not provide safe haven to militants.
